By calculating the total biomass of plants in equatorial forests and comparing that to the calculated total biomass of temperate forests, Niklas and Enquist were startled to discover the two figures came out roughly the same.

"Most people believe that tree biomass per unit area increases toward the equator and decreases rapidly toward the higher latitudes. Certainly, I thought that was true," says Niklas.

"Now, I believe that the data show there is very little difference in total tree-standing biomass across most closed-canopy forested communities. We hope this study changes a common perception."

'Biomass' is generally defined as the amount organic matter in an environment that can be converted to energy. The problem is that there are many different definitions and ways of calculating measures of biomass.

In agricultural environments, the term refers to the total mass of crops. In the context of forests, however, biomass refers to the combined weight of all plants, including trees and shrubs. Some calculations of biomass even include the mass of animals and all other organisms in an environment.

They note that equatorial forests may contain hundreds of species of plants while cool temperate forests often only contain a few dozen species, but a tree is the same regardless of where it is located. Trees compete for space and light and it doesn't matter if they are different species or not - they all grow pretty much the same way.

The implications of this study for the current debates on Greenhouse issues, calculating carbon credits and the nature of the carbon cycle are profound.

It now appears that much more carbon can be locked up in healthy forests at higher latitudes than was previously thought.

Niklas and Enquist report their findings in the April 5 edition of Nature.